The present invention relates in general to a mechanical pencil and more particularly to a lead engaging chuck mechanism which is mounted within a barrel of the mechanical pencil.
The lead engaging chuck for a mechanical pencil generally has a rear portion which receives an end of a helical spring to bias the chuck rearwardly, a lead grasping front portion or jaw portion which is generally closed to engage therein a writing lead by a radially inward force which has been converted from an axial force of the spring, and a middle portion which connects together the rear portion and the lead engaging front portion. The chuck body is formed in a unitary structure of a single piece or otherwise formed with a plurality of elements which are then assembled. In the former case of a single piece, a front portion of the chuck is provided with slits or cuts and then the slit portion is bent radially outwardly by a suitable jig or tool to form a lead gripping portion. In the latter case wherein the chuck is formed of plural separate elements, the front portion of the chuck is bent radially outwardly. In both cases, the radially outwardly inclined portion is urged radially inwardly to forcibly deform the outwardly inclined portion of the chuck to thereby provide a lead engaging force. On the other hand, when the inward thrust added to the radially outwardly inclined portion is released, the lead gripping portion of the chuck is opened automatically by its resiliency.
However, the conventional lead engaging mechanism of the chuck as described above encounters some problems. For instance, since the chuck is forcibly closed against its own resiliency during a much longer period of time than it is released, the resilient force itself becomes weaker, and finally prevents a smooth lead feed action through the chuck which does not open sufficiently due to the reduced resiliency. In order to avoid such a disadvantage, the chuck has been provided with a stronger resilient force, which however requires a stronger spring for retracting the chuck and closing the lead engaging portion against the stronger resilient force of the lead engaging portion, thereby resulting in difficulty in projecting the lead outwardly from the writing tip for writing purposes. Further, lead powder which is produced by the stronger force of the lead engaging portion is accumulated to block the lead feed action and to cause failure of lead engagement for writing purposes.